Mobile electronic instruments such as mobile telephones, mobile information terminals, and the like, are provided with a vibration generating function that notifies a mobile user, without producing a noise, that there has been a signal event, such as an incoming call, an alarm, or the like, and vibration actuators are built into mobile electronic instruments in order to produce such a function.
Linear resonant actuators (LRAs) are known as such vibration actuators that are built into such mobile electronic instruments. See, for example, Japanese Unexamined Patent Application Publication No. 2012-016153. In LRAs, a current that alternates equal to the natural vibration frequency of a weight that is suspended on a spring is supplied to interact with a magnet to cause the weight to undergo reciprocating linear vibrations in a linear direction. An eccentric rotating mass is known as a DC motor-type vibration actuator wherein an eccentric weight is attached to a shaft and the shaft is rotated to produce a vibration. See, for example, Japanese Unexamined Patent Application Publication No. H10-336949. Because LRA does not have a contact point rectifier as does ERM, the reliability and durability are higher, making it well suited to applications with high-frequency operation, such as when used for haptics in a touch panel in addition to being used as an incoming call alarm.
The vibration level in an LRA is determined by the mass of the movable element and the amplitude with which it vibrates, and thus when attempting to produce a maximum vibration level in a limited space, due to being built into a mobile electronic instrument, the amplitude of the vibration is set within the maximum range of the interior dimensions of the case, so contact between the movable element and the case is unavoidable. When the movable element contacts the case, at that time a striking sound, or a buzzing sound that is caused by the striking, is produced, and thus there is a problem in that it is not possible to satisfy the actual purpose of the vibration actuator, which is provided in order to communicate noiselessly to the mobile user that there is a signal event.
While to handle this typically a cushion material is interposed between the movable element and the case in order to mitigate the noise that is produced, this cannot completely eliminate the noise, and is not a true solution strategy. Moreover, when attempts are made structurally to avoid contact, then either the amplitude of the movable element must be made smaller relative to the case, or the case must be made larger relative to the amplitude of the movable element, making it impossible to satisfy demands for increased amplitude of vibration with a smaller size.
Moreover, there are increasing demands for mobile electronic instruments to be made thinner, such as with wearable instruments. For these, the conventional LRA is based on a structure wherein a coil is coiled around a magnet, which is a portion of the movable element, and thus there are structural limitations to the thickness that is required in order to be built into these thinner mobile electronic instruments.
In the present invention, the handling of such a situation is one example of the problem to be solved. That is, an aspect of the present invention is to, for example, provide a vibration actuator that is able to produce a large vibration amplitude with a smaller unit through the use of a mechanism wherein, fundamentally, the movable element does not strike the case, while still producing the benefit of the LRA in that it does not have a contact point rectifier, and thus can produce higher reliability and durability, to provide a thin vibration actuator that is able to respond to demands for improved thinness, and the like.